1. Field of the Invention
The invention is related to ignition systems for internal combustion engines and in particular to a direct fire ignition system which includes a sensor which detects the occurrence of a spark generated by the associated spark plug.
2. Description of the Prior Art
Direct fire ignition systems such as taught by Chrestensen in U.S. Pat. No. 3,621,826; Iwasaki in U.S. Pat. No. 4,382,430; Hamai et al in U.S. Pat. No. 4,502,454; and Fasola in U.S. Pat. No. 4,825,844 are known in the art. These direct fire ignition systems have a coil assembly attached directly to each spark plug of the engine. The coil assembly is energized by a relatively low voltage electrical pulse and generates a requisite high voltage sufficient to cause an electrical spark to be generated in the gap between the electrodes of the spark plug. The direct fire ignition systems produce the high voltage at the location of the spark plug eliminating the need for high voltages to be conducted from the distributor to the spark plug and the electrical breakdown problems associated therewith.
Warner in U.S. Pat. No. 4,090,125 discloses a direct fire ignition system in which each coil assembly has a spark sensor indirectly coupled to the secondary coil or output of the high voltage transformer. The sensor may be a sensor rod capacitively coupled to the output of the high voltage transformer or an inductive sensor loop or coil inductively coupled to the output of the high voltage transformer. The signal coupled to the spark sensor is transmitted to a remotely located detector means.
Alternatively, Noble in U.S. Pat. No. 4,846,129 discloses a direct fire ignition system having a high voltage transformer mounted on each spark plug. The primary coil of each high voltage transformer is connected to a shield. The shields are connected to each other and grounded through a common ferrite bead which generates a signal signifying that a spark has been generated. The ferrite bead is located within the driver circuits at a location remote from the high voltage transformers and their associated spark plugs. Noble also teaches the detection of auto-ignition or knock by energizing the high voltage transformer to produce a voltage which is below the voltage required to produce a spark under normal operating conditions within the cylinder, but sufficient to produce a spark when the conditions in the cylinder are conductive to auto or pre-ignition of the air fuel mixture which may be used for engine control and diagnostic purposes.